1. Field of the Invention
The present invention relates to a process for producing a dried, stable mixture of at least one alkali metal or alkaline earth metal ferrate [(VI) or (FeO.sub.4.sup.-2)] compound with alkali metal or alkaline earth metal hydroxide and carbonate compounds.
2. Background of the Invention
U.S. Pat. No. 4,307,760, which issued to Mein et al on Dec. 8, 1981, disclosed a process for recovering crystals of potassium ferrate (VI), K.sub.2 FeO.sub.4, from a residual potassium hydroxide solution by washing the crystals with a concentrated (i.e. over 30% by weight) aqueous solution of a potassium salt of an inorganic acid (e.g. K.sub.3 PO.sub.4, K.sub.2 CO.sub.3, KF, K.sub.4 P.sub.2 O.sub.7 and K.sub.2 HPO.sub.4) and at a pH greater than 9.0 to remove the residual KOH solution. After the removal of the KOH by this washing step, the ferrate product was dried in a moving air stream at 20.degree. C. to 100.degree. C. to remove the residual water. The patent states that drying converts any further residual KOH to K.sub.2 CO.sub.3, but also does not explain how this is accomplished. This patent is incorporated herein by reference in its entirety. As indicated in said Mein et al. patent, alkali metal ferrates, such as pottassium ferrate (VI), are known oxidizing agents.
This Mein et al patent urges that its recovery process is a significant improvement over the earlier recovery methods which incorporated a succession of different organic solvents such as methanol, ethanol, ethers and the like because those organic solvents may present fire, explosive and toxicity hazards as well as may react with the ferrate compounds. However, it should be noted that this process disclosed in the Mein et al patent also has problems associated with it which may hinder its commercial applicability. For instance, the use of aqueous potassium salt wash solutions increase the raw material costs for the ferrate product and present handling and recycle problems. Also, the dried product of this process may not be that stable due to the presence of water hydrates of the carbonate compounds (e.g. K.sub.2 CO.sub.3. 11/2H.sub.2 O, K.sub.2 CO.sub.3. 2H.sub.2 O) which are not readily removed with drying temperatures under 100.degree. C. Accordingly, there is a need in the art for an improved process which removes a portion of the residual hydroxide (e.g. KOH, NaOH) from the ferrate material to form a dried, stable ferrate-containing product.